package cn.cloud.all.security.crypto.encrypt;

import cn.cloud.all.security.crypto.codec.Hex;
import cn.cloud.all.security.crypto.keygen.BytesKeyGenerator;
import cn.cloud.all.security.crypto.keygen.KeyGenerators;

import java.security.spec.AlgorithmParameterSpec;

import javax.crypto.Cipher;
import javax.crypto.SecretKey;
import javax.crypto.spec.GCMParameterSpec;
import javax.crypto.spec.IvParameterSpec;
import javax.crypto.spec.PBEKeySpec;
import javax.crypto.spec.SecretKeySpec;

import static cn.cloud.all.security.crypto.EncodingUtils.concatenate;
import static cn.cloud.all.security.crypto.EncodingUtils.subArray;
import static cn.cloud.all.security.crypto.encrypt.CipherUtils.*;

public final class AesBytesEncryptor implements BytesEncryptor {

    private final SecretKey secretKey;

    private final Cipher encryptor;

    private final Cipher decryptor;

    private final BytesKeyGenerator ivGenerator;

    private CipherAlgorithm alg;

    private static final String AES_CBC_ALGORITHM = "AES/CBC/PKCS5Padding";

    private static final String AES_GCM_ALGORITHM = "AES/GCM/NoPadding";

    public enum CipherAlgorithm {

        CBC(AES_CBC_ALGORITHM, NULL_IV_GENERATOR), GCM(AES_GCM_ALGORITHM, KeyGenerators.secureRandom(16));

        private BytesKeyGenerator ivGenerator;
        private String name;

        CipherAlgorithm(String name, BytesKeyGenerator ivGenerator) {
            this.name = name;
            this.ivGenerator = ivGenerator;
        }

        @Override
        public String toString() {
            return this.name;
        }

        public AlgorithmParameterSpec getParameterSpec(byte[] iv) {
            return this == CBC ? new IvParameterSpec(iv) : new GCMParameterSpec(128, iv);
        }

        public Cipher createCipher() {
            return newCipher(this.toString());
        }

        public BytesKeyGenerator defaultIvGenerator() {
            return this.ivGenerator;
        }
    }

    public AesBytesEncryptor(String password, CharSequence salt) {
        this(password, salt, null);
    }

    public AesBytesEncryptor(String password, CharSequence salt, BytesKeyGenerator ivGenerator) {
        this(password, salt, ivGenerator, CipherAlgorithm.CBC);
    }

    public AesBytesEncryptor(String password, CharSequence salt, BytesKeyGenerator ivGenerator, CipherAlgorithm alg) {
        PBEKeySpec keySpec = new PBEKeySpec(password.toCharArray(), Hex.decode(salt), 1024, 256);
        SecretKey secretKey = newSecretKey("PBKDF2WithHmacSHA1", keySpec);
        this.secretKey = new SecretKeySpec(secretKey.getEncoded(), "AES");
        this.alg = alg;
        this.encryptor = alg.createCipher();
        this.decryptor = alg.createCipher();
        this.ivGenerator = ivGenerator != null ? ivGenerator : alg.defaultIvGenerator();
    }

    public byte[] encrypt(byte[] bytes) {
        synchronized (this.encryptor) {
            byte[] iv = this.ivGenerator.generateKey();
            initCipher(this.encryptor, Cipher.ENCRYPT_MODE, this.secretKey, this.alg.getParameterSpec(iv));
            byte[] encrypted = doFinal(this.encryptor, bytes);
            return this.ivGenerator != NULL_IV_GENERATOR ? concatenate(iv, encrypted) : encrypted;
        }
    }

    public byte[] decrypt(byte[] encryptedBytes) {
        synchronized (this.decryptor) {
            byte[] iv = iv(encryptedBytes);
            initCipher(this.decryptor, Cipher.DECRYPT_MODE, this.secretKey, this.alg.getParameterSpec(iv));
            return doFinal(
                    this.decryptor,
                    this.ivGenerator != NULL_IV_GENERATOR ? encrypted(encryptedBytes, iv.length) : encryptedBytes);
        }
    }

    // internal helpers

    private byte[] iv(byte[] encrypted) {
        return this.ivGenerator != NULL_IV_GENERATOR ? subArray(encrypted, 0, this.ivGenerator.getKeyLength()) : NULL_IV_GENERATOR.generateKey();
    }

    private byte[] encrypted(byte[] encryptedBytes, int ivLength) {
        return subArray(encryptedBytes, ivLength, encryptedBytes.length);
    }

    private static final BytesKeyGenerator NULL_IV_GENERATOR = new BytesKeyGenerator() {

        private final byte[] VALUE = new byte[16];

        public int getKeyLength() {
            return this.VALUE.length;
        }

        public byte[] generateKey() {
            return this.VALUE;
        }
    };
}
